1. Field of the Invention
The present invention relates to a zoom lens and a photographing apparatus having the zoom lens, and more particularly to a zoom lens having four lens units, as a whole, in which a lens unit of positive refractive power leads, arranged to have high optical performance over the entire range of variation of magnification by appropriately setting the lens construction of the four lens units and the zoom type, and adapted for photographic cameras, video cameras, digital cameras, still video (SV) cameras, etc.
2. Description of Related Art
Heretofore, a variety of types of zoom lenses are used with photographing apparatuses, such as photographic cameras, video cameras, etc. For example, as a zoom lens for video cameras, in Japanese Laid-Open Patent Application No. Sho 62-24213 (corresponding to U.S. Pat. No. 4,859,042), there has been proposed a four-unit zoom lens which comprises four lens units of positive, negative, positive and positive refractive powers, respectively, in order from the object side to the image side, i.e., a first lens unit of positive refractive power arranged to be stationary during zooming, a second lens unit of negative refractive power arranged as a variator lens unit to move monotonically during zooming, a third lens unit of positive refractive power arranged to be stationary during zooming and a fourth lens unit of positive refractive power arranged as an image-plane compensator lens unit to move during zooming.
In addition, in Japanese Laid-Open Patent Application No. Hei 6-27377 (corresponding to U.S. Pat. No. 6,104,548), there has been proposed a three-unit zoom lens which comprises three lens units of positive, negative and positive refractive powers, respectively, in order from the object side to the image side, i.e., a first lens unit of positive refractive power arranged to be stationary during zooming, a second lens unit of negative refractive power arranged to move during zooming and a third lens unit of positive refractive power arranged to move during zooming.
Further, in each of Japanese Laid-Open Patent Application No. Hei 5-72472 (corresponding to U.S. Pat. No. 5,572,364) and Japanese Laid-Open Patent Application No. Hei 7-270684 (corresponding to U.S. Pat. No. 5,963,378), there is disclosed a zoom lens which comprises, in order from the object side to the image side, a first lens unit of positive refractive power arranged to be stationary during the variation of magnification and during focusing, a second lens unit of negative refractive power arranged to move to effect the variation of magnification, a third lens unit of positive refractive power arranged to be stationary and having a light-condensing action, and a fourth lens unit of positive refractive power arranged to move along the optical axis to compensate for the shift of an image plane due to the variation of magnification.
In recent years, a zoom lens for use with photographing apparatuses, such as single-lens reflex cameras, video cameras, etc., is desired to have a predetermined variable magnification ratio, to include a wide angle of view and to reduce the size of the entire lens system thereof.
In the four-unit zoom lens comprising four lens units of positive, negative, positive and positive refractive powers, respectively, for video cameras, proposed in the above Japanese Laid-Open Patent Application No. Sho 62-24213, the angle of view 2xcfx89 at the wide-angle end is less than 55xc2x0 in most of the numerical examples thereof. Accordingly, a small-sized zoom lens having a wider angle of view is desired.
Further, since the variation of magnification is effected almost by moving the second lens unit only, the refractive power of each of the second lens unit and the first lens unit is made strong, and, in addition, since the compensation for the shift of the image plane is effected almost by moving the fourth lens unit only, it is difficult to suppress the variation of aberration occurring during zooming.
In general, in a zoom lens, if the refractive power of each lens unit is strengthened, the amount of movement of each lens unit required for obtaining a predetermined variable magnification ratio becomes small, so that it becomes possible to obtain a wider angle of view while shortening the total length of the entire lens system.
However, if the refractive power of each lens unit is merely strengthened, the variation of aberration due to the variation of magnification becomes large, so that, when a wider angle of view is intended to be obtained particularly, it disadvantageously becomes difficult to obtain good optical performance over the entire range of variation of magnification.
It is an object of the invention to provide a zoom lens arranged to have a wide angle of view, to have high optical performance over the entire range of variation of magnification, and to reduce the size of the entire lens system by appropriately setting the refractive power of each lens unit, the lens construction, the movement condition of each lens unit during the variation of magnification, etc., and to provide a photographing apparatus having the zoom lens.
To attain the above object, in accordance with an aspect of the invention, there is provided a zoom lens, which comprises, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, and a fourth lens unit of positive refractive power, wherein at least the second lens unit, the third lens unit and the fourth lens unit are moved in such a way that the interval between the first lens unit and the second lens unit becomes larger at the telephoto end than at the wide-angle end, the interval between the second lens unit and the third lens unit becomes smaller at the telephoto end than at the wide-angle end, and the interval between the third lens unit and the fourth lens unit becomes larger at the telephoto end than at the wide-angle end, and wherein the zoom lens satisfies the following conditions:
xe2x88x920.50 less than M4/(fTxe2x88x92fW) less than xe2x88x920.05 
0.03 less than fW/f1 less than 0.20 
0.48 less than L/fW less than 1.51 
where M4 is the amount of movement of the fourth lens unit from the wide-angle end to the telephoto end during zooming, fW and fT are the focal lengths of the zoom lens at the wide-angle end and the telephoto end, respectively, f1 is the focal length of the first lens unit, and L is an interval on an optical axis at the wide-angle end between a lens surface having the smallest refractive power among lens surfaces included in the third lens unit and a lens surface having the largest refractive power among lens surfaces included in the fourth lens unit.
In the zoom lens according to the above aspect of the invention, the amount of movement M4 of the fourth lens unit from the wide-angle end to the telephoto end during zooming takes a positive sign when the fourth lens unit moves in a direction toward the image side. Further, the smallest refractive power and the largest refractive power of the lens surfaces included in the third lens unit and the fourth lens unit are determined with positive or negative signs thereof taken into consideration, and the negative refractive power is assumed to become smaller accordingly as the absolute value thereof becomes larger, and is assumed to be smaller than a positive refractive power having any absolute value.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.